1. Field of the Invention
The present invention relates to a process for producing .alpha.-hydroxy-isobutyramide, and more particularly, to a process for producing .alpha.-hydroxy-isobutyramide (hereinafter referred to as "HAM") by reacting continuously acetone cyanohydrin (hereinafter referred to as "ACH") with water.
2. Description of the Related Art
It is known that in general, amide compounds can be produced by the reaction of the corresponding nitrile compounds with water, and various catalysts effective for this reaction are also known.
Manganese dioxide disclosed in U.S. Pat. No. 3,366,639 is one such catalyst. Copper-containing catalysts often used for hydration of nitrile compounds are quite insufficiently effective for the hydration of .alpha.-hydroxynitrile compounds such as ACH and the like. On the contrary, manganese dioxide gives a fairly good result in the hydration of ACH as shown in West German Patent Laid-open No. 2,131,813.
Japanese Patent Application Laid-open No. Sho 52-222 (U.S. Pat. No. 4,018,829) discloses that the yield of HAM can be enhanced by adding acetone to the reaction mixture in a method for producing HAM by the hydration of ACH in the presence of manganese dioxide as a catalyst at 60.degree.-90.degree. C.
Japanese Patent Application Laid-open No. Sho 63-57535 discloses that fluctuation of the catalytic activity can be eliminated and the performance of the catalyst can be improved by using a manganese dioxide prepare from a heptavalent manganate and a hydrohalogenic acid.
However, according to the present inventors' investigation on Japanese Patent Application Laid-open No. Sho 52-222 (U.S. Pat. No. 4,018,829), it has been found that the catalytic activity is rapidly decreased with the lapse of time according to the industrial continuous method for producing HAM by the hydration of ACH in a solvent, i.e. an aqueous acetone, using a catalyst-suspension type reactor.
A method for solving the above-mentioned problem is shown in Japanese Patent Application Laid-open No. Hei 2-196763, that is, the decrease in the catalyst activity is suppressed by adjusting the hydrogen ion concentration (pH) of the liquid starting material mixture fed to the reactor to 4-8. However, it is not clearly explained referring to working examples whether this method can suppress the decrease in catalytic activity for a long period of time exceeding one week.
Further, in order to extend the life of manganese dioxide catalysts, Japanese Patent Application Laid-open No. Hei 3-68447 discloses an improvement in the preparation of a manganese dioxide catalyst, and U.S. Pat. No. 4,987,256 and European Patent Application Publication No. 461,850 disclose that a second component is added to manganese dioxide. These methods give some effects, but the life of the manganese dioxide thus prolonged is not always sufficient.
In view of the foregoing, when HAM is continuously produced in industry by hydrating ACH, manganese dioxide catalysts are deteriorated or deactivated resulting in frequent change of the catalysts and thereby, catalyst costs increase. Therefore, it is one of the biggest problems to maintain the activity of manganese dioxide catalysts for a long period of time.